Having dismissed rigid/fixed
sidecars during my Bicycle
sidecar project, I decided to make this copy of
a 1980's BMX sidehack to see what it was like to ride.

The donor bike for this project
was not actually a BMX, but rather a child's bicycle with 20" wheels.
This had a frame which was a little shorter than a BMX frame but had
the advantage of 5 gears.

The first modification was to
weld two steel plates on either side of the head stock tube as shown.
These plates were then drilled right through with a 25mm hole cutter.

The material chosen to construct
the side car was 25mm and 20mm steel conduit. This was chosen for two
reasons.

First of all there was some being
discarded in a nearby skip (make sure you ask before taking it though).

Secondly this allowed the use of
a commercial pipe bender to form the frame. The pipe bender was rented
for a day from the local tool hire shop.

Hired pipe bender

The following photograph sequence
gives and idea of the construction method.

First a piece of pipe with two
bends was made to give the outside frame of the sidecar.

Some blocks of wood were cut to
be used as jacks to set the height of the side car floor and the bike
was held upright against the wall using a clamp on the rear tyre.

The height of the sidecar was
150mm from the ground. This should give some ground clearance whilst
maintaining a low centre of gravity.

Next the inner frame was made
with a single bend to match the outer frame and this was brazed in
place.

The front handle was made with 2
bends which were not quite 90º, so that the sides were slopping in
towards the top. It was not possible to get the bends in the right
place to align with the spacing at the bottom, so in the end the handle
was cut into two parts and these were joined with a slug of steel along
the top edge. This join would be covered with handlebar tape.

The side handles were bent as a
matching pair. They were made from smaller 20mm conduit, as this was
all that was available.

This photo also shows the front,
lower crosspiece in place.

With all the bending complete, an
off-cut of 25mm conduit was bent to create an offset seat post, in case
the bike was too short for the rider.

Then the pipe bender was returned
to the hire shop.

The front mounting through the
two welded plates used the part shown on the right. This was
manufactured from steel bar.

The Dimension 'x' was just shy of
the gap between the outside of the two frame plates so that a bolt in
the M12 hole would pull up tight and hold the mount securely.

The hole was continued right
through the part to try and make it a bit lighter.

The rear mount was made from
steel plate. It was a simple angled part welded in situ to ensure an
aligned fit. The vertical arm was angled forward to reach the rear
wheel.

The outside wheel was cantilever
mounted on a strip of steel which was taken from an old woodworking
cramp (which was bent and useless).

As the sides of the passenger
compartment were sloped, to get the wheel vertical the steel strip was
mounted in the inside of the lower bar but the outside of the upper bar
as shown on the right. An extra wheel nut was used between the wheel
and mounting strip to space the wheel away from the frame.

The first position chosen for the
sidecar wheel was too far forward. This gave good straight running but
too much tyre scrub when turning. So the wheel was moved back so that
it was about 50mm forward of the driving wheel. This position gave a
good compromise between stability and cornering ability.

The new Bike fitted with the
sidecar.

A quick road test confirmed that
the sidecar was good, but the bike was way too small for the rider,
despite the cranked seat post.

Luckily my Nephew was discarding
a larger BMX bike - still not quite full size but much longer.

The front mounting on the sidecar
was retained, but this bike had a square down tube so this was just
drilled through and fitted with a sleeve to suit the front mount,
rather than using the addition of welded plates.

The rear mounting had to be
remade with a more vertical support arm to accommodate the longer wheel
base. The rear mount was also re-enforced with an angled brace for
extra strength.

The sidecar is shown here painted
in satin white.

Some garden mesh was riveted to
the wheel side to protect the passenger and some aluminium tread plate
was riveted to the base. This plate was 4.5mm thick and so required no
extra support underneath.

The bike was painted in the same
colour as the sidecar and this photo shows it after final assembly late
one night.

Handlebar tape was added to the
front and inside handle of the sidecar.

Click for larger image

These images show the finished
construction. Click any image for a larger view.